You need a matech buis (or replica) and then you are done. Also, it isn't inaccurate but that grip is really more popular for those with the M16s with longer (heavier) rifles. M4 peoples have more traditional vertical forward grips. But I am sure there will be a thousand pictures to prove me wrong.
What kind of sling system are you using. Armorers like to put one-point sling adapters on the backend of the receiver, the manufacturer varies from unit to unit.
okay hope that helps.